1. Field of the Invention
The present invention relates to an image stabilizing apparatus comprising a plurality of optical blur suppression means moved to deflect beams and perform blur suppression, and a plurality of holding means for holding the optical blur suppression means at predetermined positions.
2. Related Background Art
In recent years, image recording devices such as a silver camera and a video camera have been automated, and various functions such as an automatic exposure control means and an automatic focus control means have been put into practice.
In particular, an image recording device such as a video camera generally uses a zoom lens as a photographic lens, and the zoom ratio of the zoom lens is increasing year by year.
On the other hand, the sizes of the image recording devices are also decreasing, and even a compact camera which can be operated by one hand has been introduced on the market along with a reduction in size of the image recording frame size and developments of high-density integration techniques and compact recorder mechanical chassis.
Disturbing frame blurring caused by hand vibrations of a photographer often occurs in use of a compact video camera having such a zoom lens. Various blur suppressing apparatuses have been proposed to eliminate this blurring and obtain a stable frame. Such a blur suppressing apparatus can greatly suppress hand vibrations generated in photography even with a tripod on a ship or motor vehicle as well as the disturbing frame blurring caused by hand vibrations.
This blur suppressing apparatus includes at least a vibration detection means for detecting a blur and a vibration suppression means for suppressing the image blur so as to prevent frame blurring in accordance with information of the detected vibration.
Examples of the vibration detection means are an angular accelerometer, an angular speedometer, and an angular displacement meter. Examples of the blur suppression means are a method using a variable apex angle prism (to be described in detail later) proposed by the present applicant and a method of sequentially changing (tracking) an extraction position to a position (at which the blur is suppressed) in a video camera arranged such that an area used as an actual frame is extracted from the obtained photographic frame information.
The former method as the blur suppression means using the variable apex angle prism or any other optical means to eliminate the blur of an image to be focused on an image pickup element is called an optical correction means, whereas the latter method as the blur suppression means for electronically processing image information including a vibration is called an electronic correction means.
The optical correction means can generally suppress a vibration within the vibration angle range of the camera regardless of the focal length of the lens. Therefore, the image blur can be eliminated even at a large focal length on the telephoto side of the zoom lens to a negligible degree in practice. However, the optical correction means undesirably results in a bulky camera.
To the contrary, the electronic correction means has a constant suppression ratio with respect to, e.g., the vertical size of the frame, on the frame. For this reason, when the focal length on the telephoto side is increased, the blur suppression performance is degraded. The electronic correction means is advantageously employed for a compact arrangement.
FIGS. 9A to 9C are views for explaining the relationship between the focal length and the camera vibration angle with respect to object positions on the frame.
Referring to FIG. 9A, an optical axis 113 is obtained when a camera is located at a position 112. In this case, the face of a person 111 as an object to be photographed is located at almost the center of the frame. Assume that the camera is rotated through an angle a by a hand vibration. At this time, a camera position 114 and its optical axis 115 are set.
FIGS. 9B and 9C show frame positions at the camera positions 112 and 114. More specifically, FIG. 9B shows a state at the telephoto end of a zoom lens, and FIG. 9C shows a state at the wide-angle end of the zoom lens. Objects 116 are located at frame positions in these states, as shown in FIGS. 9B and 9C. Frames 117 and 119 are set at the camera position 112, whereas frames 118 and 120 are set at the camera position 114.
As is apparent from FIGS. 9A to 9C, frame blurring at a large focal length of the lens is worse than that at a small focal length if the camera is vibrated through the same angle a. Therefore, an optical means such as a variable apex angle prism is effective as a blur suppression means to be combined with a lens having a large focal length at the telephoto end.
FIGS. 10A to 10C show the arrangement of a variable apex angle prism.
Referring to FIGS. 10A to 10C, the variable apex angle prism comprises glass plates 121 and 123 and a bellows portion 127 made of, e.g., polyethylene. A transparent liquid 122 consisting of, e.g., silicone oil is sealed inside the space defined by the glass plates 121 and 123 and the bellows portion 127.
FIG. 10B shows a state in which the two glass plates 121 and 123 are parallel to each other. In this case, the incident angle of a ray on the variable apex angle prism is equal to the exit angle of the ray. However, when the glass plates 121 and 123 are inclined with each other at angles shown in FIGS. 10A and 10C, rays 124 and 126 are diffracted at given angles.
When the camera is inclined by a hand vibration or the like, the angle of the variable apex angle prism arranged in front of the lens is controlled so that the ray is diffracted by an amount corresponding to the inclination angle of the camera, thereby eliminating the image blur.
FIGS. 11A and 11B show a blur suppression operation. FIG. 11A shows a state wherein the glass plates of the variable apex prism are parallel to each other, and the ray corresponds to the head of the object 116. As shown in FIG. 11B, the variable apex angle prism is driven by an amount corresponding to the angle a to diffract the ray, so that the photographic optical axis is constantly aligned with the head of the object 116.
FIG. 12 is a view showing the practical structure of a variable apex angle prism unit including the variable apex angle prism, actuators for driving the variable apex angle prism, and apex angle sensors for detecting the angular state of the variable apex prism.
Since actual vibrations occur in all directions, the front and rear glass surfaces are arranged to be rotatable about rotational axes shifted by 90.degree.. In this case, suffixes a and b represent constituent parts representing these two rotational directions, and the same numbers denote the same functions. Some parts represented by the suffix b are not illustrated.
A variable apex angle prism 141 includes the glass plates 121 and 123, the bellows portion 127, and a liquid. The glass plates 121 and 123 are integrally mounted on holding frames 128a and 128b through an adhesive or the like. The holding frames 128a and 128b constitute rotational axes 133a and 133b with fixed parts (not shown) and are rotatable about the rotational axes 133a and 133b, respectively. The rotational direction of the rotational axis 133a is shifted from that of the rotational axis 133b by 90.degree.. A coil 135a is integrally mounted on the holding frame 128a. Magnets 136a and yokes 137a and 138a are mounted on a fixed portion (not shown). When a current is supplied to the coil 135a, the variable apex angle prism 141 is pivoted about the rotational axis 133a. A slit 129a is formed at the distal end of an arm 130a integrally extending from the holding frame 128a, thereby constituting the apex angle sensor between a light-emitting element 131a such as an IRED and a light-receiving element 142a such as a PSD, which elements are arranged on a fixed portion.
FIG. 13 is a block diagram showing an image stabilizing apparatus having the variable apex angle prism 141 as a blur suppression means in combination with a lens.
Referring to FIG. 13, this image blur preventive apparatus includes the variable apex angle prism 141, apex angle sensors 143 and 144, amplifiers 153 and 154 for amplifying outputs from the apex angle sensors 143 and 144, a microcomputer 145, vibration detectors 146 and 147 each including an angular accelerometer, and actuators 148 and 149 including parts from the coil 135a to the yoke 138a. The variable apex angle prism 141 is located in front of a lens 152.
The microcomputer 145 determines currents to be supplied to the actuators 148 and 149 to control the variable apex angle prism 141 at an optimal angle for eliminating the blur in accordance with the angular states detected by the apex angle sensors 143 and 144 and the detection results from the vibration detectors 146 and 147.
Note that the main components are constituted by pairs of blocks to independently perform control operations in two directions perpendicular to each other.
The conventional image stabilizing apparatus using the variable apex angle prism as the blur suppressing means has been described above. As another example comprising an optical correction means, U.S. Ser. No. 516,303 (EP Provisional Publication No. 396,981) by the present applicant discloses an image blur preventive apparatus having a lens group which is arranged in front of the photographic lens and swung by the inertia.
When this optical correction means is used, the chromatic aberration tends to increase when the correction angle of the optical axis is increased. In order to prevent degradation of the image quality in an inoperative state of the image blur preventive apparatus, the optical correction means must be kept held at a position where chromatic aberration does not occur (minimum). This position is defined as a position where the correction angle of the optical axis is 0.degree..
The apparatus employing the variable apex angle prism as the blur suppressing means is taken into consideration again. As shown in FIG. 9B, the variable apex angle prism must be set so that the two glass plates 121 and 123 are parallel to each other and is perpendicular to an optical axis 125 in an inoperative state of the blur preventive apparatus.
The following two methods are available to hold the variable apex angle prism in this state.
1) The actuators are energized to keep the two glass plates parallel to each other.
2) The two glass plates are mechanically kept parallel to each other.
According to the method 1), in the block diagram of FIG. 13, outputs from the vibration detectors 146 and 147, fetched by the microcomputer 145, are disabled. A feedback loop is formed such that a position corresponding to the parallel state of the two glass plates is given as a target position.
FIG. 14 is a block diagram for realizing control by the method 1). For the sake of descriptive simplicity, an arrangement in only one direction is illustrated.
When a photographer selects an operative/inoperative state of the blur preventive apparatus, this selection result is fetched to the microcomputer 145. In the operative state, a target position selection means (select target position) 156 selects an output A.sub.1 as a target position A from the vibration detector 146. In the inoperative state, the target position selection means (select target position) 156 selects an output A.sub.0 as the target position A from the apex angle sensor 143, which corresponds to the parallel state of the glass plates of the variable apex angle prism 141. The angular state of the variable apex angle prism 141 is detected by the apex angle sensor 143 and is amplified by the amplifier 153. An output from the amplifier 153 is extracted as a displacement output A'. A predetermined gain is multiplied with a difference between the target position A and the displacement output A', and the product is fed back to the actuator 148, thereby maintaining the apex angle state at the target position A.
An arrangement for the method of mechanically holding the parallel state of the glass plates of the variable apex angle prism is shown in FIGS. 15A and 15B.
The holding frames 128a and 128b shown in FIG. 12 have projections. A lever 159 for maintaining the parallel state of the glass plates integrally has holding portions 160a and 160b for holding the projections of the holding frames 128a and 128b. A gear 161 is mounted on the rear end portion of the lever 159. The gear 161 is meshed with an output gear 162 of a motor 163. Upon rotation of the motor 163, the lever 159 is rotated.
FIG. 15B is a view showing the mechanism when viewed from an arrow in FIG. 15A. The position of the holding portion 160a indicates the parallel state wherein the glass plates are parallel to each other. When the holding portion 160a is located at a position indicated by the alternate long and two short dashed line, the glass plates are set in a free state. The parallel or free state can be easily detected by a combination of sensors such as a photointerrupter and a leaf switch.
When a method of optimally holding the blur suppression means at an optimal position in an inoperative state of the blur preventive apparatus is taken consideration, the following problems are posed.
1. When the method 1) is employed, power almost equal to that in an operative state of the blur preventive apparatus is wasted although the blur preventive apparatus is kept in an inoperative state.
2. When the method 1) is employed and an abrupt vibration acts on the video camera, an optimal state may not be maintained depending on the characteristics of the feedback system.
3. When the method 2) is employed, large motor noise is produced during switching between the parallel state and the free state, or collision noise between the holding portion 160 and the holding frame 128 is produced. When such noise is produced during recording in a video camera, it may be undesirably recorded.
4. When the method 2) is employed, the following drawbacks are caused. Since the stable position of the variable apex angle prism is greatly different from a predetermined position (neutral position) held by the holding means due to the gravitational influence (since the liquid inside the transparent glass plates normally receives the gravitational influence, the transparent glass plates are located in an inverted V shape), when the holding means changes from the holding state to the holding release state, or vice versa, the photographic frame is greatly moved, or the photographic frame becomes discontinuous due to the collision (during the change from the holding release state to the holding state) of the variable apex angle prism against the holding means, thereby degrading the photographic frame or damaging the holding means and the variable apex angle prism.
5. When the method 2) is employed, when the variable apex angle prism is moved to the neutral position during the change from the holding state to the holding release state (more specifically, at the start of blur suppression immediately after the release of the holding state), large instantaneous currents must be supplied to the actuators 148 and 149.